Timing Marks on the 273 [66 Barracuda]
Is your car a CAP car?
If so it might have a gismo like this.
If so the advance curve is very different then non CAP cars.
The 67 273 with CAP calls for 5 deg ATDC.which is very different than non CAP.
If you set it a 0 or 5 BTDC you should be ok to start.
Also if when you reattach the vacuum advance the engine speeds up there is carborator tuning that needs to be done.